Method of making induction-motor squirrel cages



Sept. 5, 1961 F. B. M LAREN METHOD OF MAKING INDUCTION-MOTOR SQUIRREL CAGES Filed May 13, 1957 mvsmon -l fiefosexk 8. Mac Z 424W 7 Patented Sept. 5, 1961 2,998,638 METHOD OF MAKING INDUCTION-MOTOR SQUIRREL CAGES Frederick B. MacLaren, New York, N.Y., assignor, by mesne assignments, to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware Filed May 13, 1957, Ser. No. 658,753 2 Claims. (Cl. 291'55.53)

My invention relates to a method of making induction-motor, squirrel cages and more particularly to an improved method of making induction-motor, squirrel cages which reduces the number of defective squirrel cages produced by methods of the prior art.

In the prior art induction-motor, squirrel cages usually are cast from aluminum. In the practice of this method a number of toothed laminations are assembled on an arbor with their slots disposed to provide rotor slots having the desired skew. The stack of assembled laminations is placed in a mold. Molten aluminum, or the like, is poured into the mold as the entire assembly is spun on the arbor axis. The centrifugal force resulting from the spinning acts on the molten aluminum to force air out of the mold and to fill the end plate spaces and the rotor slots. When the aluminum solidifies, the cast rotor is forced out of the mold and finished in a manner known to the art. Ideally, the centrifugal force of spinning pushes all the air out of the mold. It has been found in practice, however, that bubbles of air become trapped in the bottoms of some of the rotor slots to result in rotor bars having irregular cross sections. Asa result of these irregularities, the rotor current is low. Consequently machines having rotors cast by the method of the prior art may be rejected because of failure to meet their torque requirements.

In the manufacture of an induction motor having a laminated rotor the core laminations are insulated from each other to minimize eddy-curent loss. In the casting method of forming induction-motor, squirrel cages, the heat of the molten metal may deleteriously afiect this into form straight slots having no skew. I broach or otherwise out the inner surface of a tube of aluminum or the like to form a plurality of internal, axially-extend ing grooves separated by lands. The lands and grooves of the cylinder are formed to be complementary to the respective slots and teeth of the lamination stack. I force the stack of laminations into the tube, the length of which is such that the tube ends slightly overhang the stack ends. I next spin down the tube ends to form the rotor end plates. As a final step I machine the outer surface of the tube to form the finished rotor.

In the accompanying drawings which form part of the instant specification .and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIGURE 1 is a perspective view of a broached tube and a stack of laminations illustrating the initial steps of my method of making inductiommotor, squirrel cages.

FIGURE 2 is a perspective View illustrating an inter? mediate step in my method of making induction-motor, squirrel cages.

FIGURE 3 is a perspective view of a stack of laminationsinserted in a broached tube in accordance with my method of making induction-motor, squirrel cages.

FIGURE 4 is' a perspective view of a completed squirrel cage rotor made by my method ofmaking induction-motor, squirrel cages.

Referring now more particularly to the drawings, in the practice of my'method I first assemble a plurality of laminations 10 on an arbor 12 by means of 'a key 14;

terlamination insulation, producing a consequent increase I in eddy-current loss in the finished motor.

I have invented an improved method for making induction-motor, squirrel cages which overcomes the disadvantages of the prior art discussed hereinabove. My method ensures that all bars of the squirrel cage rotor have the required uniform cross section. My method is simple and may be practiced in an expeditious manner. It does not require handling of any molten material. My method is a cold process which will not injure the insulating material between the core laminations.

One object of my invention is to provide a method of making induction-motor, squirrel cages which represents an improvement over methods of the prior art.

Another object of my invention is to provide a method of making induction-motor, squirrel cages which ensures that the squirrel cage bars have the uniform cross section necessary to produce the required torque in the finished motor.

A further object of my invention is to provide a method of making induction-motor, squirrel cages which is simple and which may expeditiously be performed.

Yet another object of my invention is to provide a cold process for making induction-motor, squirrel cages.

Other and further objects of my invention will appear from the following description:

In general my invention contemplates the provision of a method of making induction-motor, squirrel cages in which I first stack a plurality of toothed laminations of magnetic material on an arbor. I employ any convenient means, such as a key, to align the lamination teeth Each lamination is formed with a number of peripheral teeth 16. Key 14 holds the laminations 10 on arbor -12 with the teeth 16 aligned to form anumber of axially: extending, rotor slots 18 in the stack of laminations on the arbor.

I broach or otherwise form a number of grooves 20 in the interior of a tube 22 made of drawn aluminum or another suitable material. Lands 24 separate adjacent grooves20. The number of grooves 20 in. the interior of tube 22' correspondsto the nrumberof teeth 16 in the respective laminations 10 assembled on arbor 12. The inner diameter of the tube 22 before broaching is the same as the diameter of a lamination 10 measured be tween the bases of a pair of opposite slots 18. The outer diameter of the tube is somewhat greater than the diameter of a lamination measured between the outer edges of a pair of opposite teeth. Tube 22 is slightly longer than the stack of laminations for a reason which will be explained in detail hereinafter. It is to be understood that I may, if desired, form tube 22 and grooves 20 by the less expensive, though less accurate, extrusion process. Other materials such as copper or brass could be employed to form the tube.

After having assembled the stack of laminations 10 on arbor 12 with the teeth aligned to form slots 18 and after forming the grooves 20 in the tube 22, I insert the stack of laminations into the tube so that the lands 24 fit closely in the slots 18 of the stack of laminations. As has been pointed out hereinabove, tube 22 has a length slightly greater than the length of the stack of laminations to overhang the stack at the ends.

After having inserted the stack oat laminations into the tube 22 in the manner shown in FIGURE 2 to form the assembly shown in FIGURE 3, I next form the rotor end plates. I accomplish this by spinning down the overhanging ends of tube 22 over the ends of the stack of laminations to form the rotor end plates, one of which plates 26 is shown in FIGURE 4. This spinning operation may be performed on a suitable machine tool, such as a spinning lathe. 1

When the spinning operation has been completed to form the rotor and plates, I machine the outer surface of tube 22 to expose the laminations to finish the rotor to the form shown in FIGURE 4. From the foregoing it will be understood that the lands 24- formed in tube 22 provide the bars in the finished squirrel cage rotor.

It will be seen that the rotor bars of the rotor made according to my method have no skew. Customarily, in the prior art some skew is provided in the rotor bars. This skew may, however, be provided in the machine stator, in which case the rotor bars may be straight. In my method I form a rotor having straight bars 24 and provide skew in the machine stator. It is to be understood that I may, if desired, form skewed slots 20 to form skewed rotor bars. Preferably I form straight slots since it is less expensive.

In the practice of my method I first broach tube 22 and stack laminations 10 on arbor 12 as shown in FIGURE 1. When these operations are complete I insert the stack of laminations 10 into the tube 22 with the lands 24 fitting into the slots 18. I spin the over hanging ends of the tube 22 down over the ends of the stack of laminations to form the end plates, such as plate 26, of the rotor. After spinning down the tube ends, I machine the outer surface of the tube to complete the rotor. It will be appreciated that the lands 24 have substantially uniform cross-sections and that they substantially completely fill the slots 18. As a result, a machine having a rotor made according to my method will not fail for low torque owing to irregular bar cross section.

It is noted further that my method does not involve the use of heat which may deleteriously affect the insulation between the rotor laminations.

It will be seen that I have accomplished the objects of my invention. I have provided a method for making induction-motor, squirrel cages which overcome defects of the method of the prior art. My method ensures that the rotor bars have substantially uniform cross sections. My method is easy and simple to practice. It does not require handling of any molten metal. My method is a cold process.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcomhinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

l. A method of making an induction-motor squirrel cage rotor including the steps of forming a plurality of longitudinally extending grooves along the inner surface of a metal tube, assembling a stack of laminations each having a number of teeth equal to the number of said grooves on an arbor with their teeth aligned, moving said tube over said stacked laminations with said teeth aligned in the tube grooves, spinning down the ends of said tube to form rotor end plates and reducing the circumference of said tube by removing metal from the tube wall to expose the edges of said lamination teeth.

2. A method of making an induction-motor squirrel cage rotor including the steps of forming a plurality of longitudinally extending grooves along the inner surface of a metal tube, assembling a stack of laminations each having a number of teeth equal to the number of said grooves on an arbor with their teeth aligned, moving said tube over said stacked laminations with said teeth aligned in the tube grooves, forming annular rings from the ends of said tube to provide rotor end plates and reducing the circumference of said tube by removing metal from the tube wall to expose the edges of said lamination teeth.

References Cited in the file of this patent UNITED STATES PATENTS 1,711,414 Kanaky Apr. 30, 1929 2,104,141 Stevens Ian. 4, 1938 2,138,661 Maxwell Nov. 29, 1938 2,192,434 Critchfield Mar. 5, 1940 2,387,073 Horlacher Oct. 16, 1945 2,411,684 Hamilton et a1. Nov. 26, 1946 2,528,154 Ludwig et al. Oct. 31, 1950 2,648,123 Phillips Aug. 11, 1953 2,834,095 Lazzopina et al. May 13, 1958 

